A database server configured for retrieval through a network comprises a computer incorporating a high-speed CPU provided with a high-capacity storage device, a network operation system and application software dedicated to database server operation. To this database server, a clienat machine is connected via the network. The clienant machine issues a retrieval command via the network, upon which retrieval is made in the database server. A retrieval result data is then transmitted to the client machine via the network.
For extensive use of the database, the database server is connected with a multiple number of client machines via a wide-area network such as Internet, a LAN in a company, and so on. The connection of the client machines and the database server with Internet can be provided by a telephone link, as well as high-speed digital data transmission link, dedicated communication link, and so on. TCP/IP communication protocol is used as the world standard for the information exchange.
Kind of data retrieved in the database is very extensive, and so are attributes of the data retrieved. Information retrieved from the database takes a form of a table, in which a number of data is arranged in a matrix. The table is made up of a number of rows having a same structure. Each of the rows represents a unit of information, serving as a minimum unit of the result of retrieval in the database. Each of the rows contains items, and the item represents a minimum unit of information handled by the database.
When the result of retrieval obtained by the server side is transmitted to the client machine, a cycle of transmitting operation is performed for each item or row. This means that a huge amount of time must be spent for the transmitting procedure if the retrieved data includes a large number of rows.
There is another problem when the data is transmitted via a general-purpose network such as Internet. Specifically, the link is shared by other users, which means a long transmission time is required if the link is being used by a large number of users. The transmission time can be longer if the communication link has a narrow bandwidth, making impossible to use the database efficiently. For these reasons, very often, the retrieval speed decreases very unfavorably via a public link such as Internet, even if the same data retrieval can be performed at a very high speed on an in-house LAN.
An invention disclosed in the Japanese Patent laid-Open No. 8-286889 proposes a data transmission method, in which only a difference contained in an intended data is transmitted, and the client machine restores the intended data from a previously transmitted data and the difference data.
Further, an invention disclosed in the Japanese Patent laid-Open No. 9-198285 proposes an arrangement, in which access operation from the client machine to the database on the server and transmission operation of data other than the database data are performed by using a same language and interface as used in execution of functions uniquely incorporated in an application software as the subject of development.
Data retrieved from the database is very extensive. In addition, attribute of retrieved data and size of the retrieval data table are different every time the retrieval is made. Therefore, the data transmission method in which a predetermined data table format is stored in the client machine and only a difference data contained in an intended data is transmitted does not have general applicability. Further, the data retrieved in accordance with the retrieval command must eventually be transmitted in its entirety. Therefore, the data transmission method disclosed in the first Gazette can not increase data transmission speed.
On the other hand, the invention disclosed in the second Gazette aims at improving transmission efficiency by rationalizing the way in which the database is used. In other words, nothing has been changed in the method of data transmission, configuration of the data to be transmitted, and so on. Therefore, there is no improvement in data transmission speed itself, and the data transmission speed can be decreased dramatically depending upon a condition of the communication link.